Methods of forming a pattern in a material and methods of forming openings in a material to be patterned

ABSTRACT

Methods of forming a pattern in a material and methods of forming openings in a material to be patterned are disclosed, such as a method that includes exposing first portions of a first material to radiation through at least two apertures of a mask arranged over the first material, shifting the mask so that the at least two apertures overlap a portion of the first portions of the first material, and exposing second portions of the first material to radiation through the at least two apertures. The first portions and the second portions will overlap in such a way that non-exposed portions of the first material are arranged between the first portions and second portions. The non-exposed or exposed portions of the first material may then be removed. The remaining first material may be used as a photoresist mask to form vias in an integrated circuit. The pattern of vias produced have the capability to exceed the current imaging resolution of a single exposure treatment.

FIELD OF THE INVENTION

Embodiments described herein relate generally to the fabrication ofintegrated circuits, and more specifically, at least one embodimentrelates to the fabrication of vias in an integrated circuit usingmultiple exposures.

BACKGROUND OF THE INVENTION

Electrically conductive lines and connections form many commoncomponents of integrated circuits. Dynamic random access memory (DRAM)circuitry, for example, incorporates multiple parallel conductive linesto form word-lines and bit-lines, which are connected by electricalconnectors to various components. In order to increase capacity andaccommodate smaller devices, there is constant pressure to increase thedensity of components on these and other circuits. The continualreduction in feature size places greater demands on the techniques usedto form the features.

Photolithography is a commonly used technique for patterning integratedcircuit features, such as conductive lines and vias that may be filledwith a conductive material to form a connection. One example of aphotolithographic method for patterning integrated circuit featuresincludes depositing a photoresist material over a material to bepatterned, covering portions of the photoresist material with a mask,exposing the uncovered photoresist material to light, and etching awayeither the exposed portion, in the case of a positive resist, or theunexposed portion of the photoresist material, in the case of a negativeresist. The remaining photoresist material is used as an etch mask foran etching process. In the etching process, portions of the of thematerial to be etched that are not covered by the photoresist materialare removed by, for example, wet or dry chemical etch. After the etch,the remaining photoresist material is dissolved.

There are, however, limitations on how close features, such as vias inwhich electrical connectors may be formed, can be patterned using knownphotolithographic techniques. The size of features on an integratedcircuit are conventionally described by their “pitch,” which is thedistance between an identical point on two neighboring features. Due toan inherent resolution limit, which is a function of a numericalaperture of the mask and the wavelength of the light used, there is aminimum pitch below which features cannot be reliably formed usingconventional photolithographic techniques.

Thus, there exists a need for a method and apparatus to pattern closelyspaced features, e.g., vias, which may include electrical contacts,having a smaller pitch than would be possible using a mask having agiven resolution limit in a conventional photolithographic technique.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 through 9 illustrate steps in a photolithographic method offorming vias in a substrate using a first mask embodiment according toan embodiment described herein.

FIG. 10 illustrates a mask in accordance with another mask embodimentdescribed herein that may be used in the method described with referenceto FIGS. 1-9.

FIG. 11 illustrates a mask in accordance with another mask embodimentdescribed herein that may be used in the method described with referenceto FIGS. 1-9.

FIG. 12 illustrates a mask in accordance with another mask embodimentdescribed herein that may be used in the method described with referenceto FIGS. 1-9.

FIG. 13 illustrates a mask in accordance with another mask embodimentdescribed herein that may be used in the method described with referenceto FIGS. 1-9.

DETAILED DESCRIPTION

The term “substrate” in the following description refers to anysupporting material suitable for fabricating an integrated circuit,typically a semiconductor material, but not necessarily so. A substratemay be silicon-based, may include epitaxial layers of silicon supportedby a base semiconductor foundation, may be a layer of semiconductormaterial itself, can be sapphire-based, silicon-on-insulator (SOI),metal, polymer, quartz, or any other materials suitable for supportingan integrated circuit or mask formation. When reference is made to asemiconductor substrate in the following description, previous processsteps may have been utilized to form regions or junctions in or over abase semiconductor. The terms “removable” and “non-removable” as usedherein relate to portions of a material that either will be removed orwill not be removed, respectively, by a subsequent step, for example bytreating the material with a solvent.

In various embodiments described herein, a mask having a pattern is usedduring a first exposure of a photoresist material. The mask is shiftedand a second exposure of the photoresist is performed. The first andsecond exposures overlap to yield a grid of non-exposed areas on thephotoresist, which may be removed using a negative develop technique. Invarious embodiments, the non-exposed areas may be etched into vias to befilled with conductive material and used, e.g., as electrical contactsto connect to closely spaced access lines, such as access lines,data/source lines, bit-lines, etc. The pattern of vias produced has thecapability to exceed the current resolution of a prior art singleexposure treatment. The disclosed embodiments are particularly wellsuited for application to processor and memory technologies, such as,e.g., dynamic random access memory (DRAM) and other memory devices. Thedisclosed embodiments are also suitable for other integrated circuitstructures having closely spaced electrical contacts. It should beunderstood that the embodiments discussed herein are not limited by theexamples described herein and that changes can be made thereto.

An example embodiment is now described with reference to theaccompanying figures wherein like reference numbers are usedconsistently for like features throughout the drawings. FIGS. 1-9 showsteps in a method of making a grid of vias according to an embodimentdescribed herein.

FIG. 1 illustrates a top down view and FIG. 2 shows a cut-away side viewalong line A-A of a mask 110 arranged over a stack of materialsincluding a substrate 150, a conductive material 140 layer, such as ametal or a metal silicide, a dielectric material 130, such as an oxide,and a negative photoresist material 120, such as SU-8. The conductivelayer 140 may include, for example, a single layer of conductivematerial or may include a plurality of conductive lines. It should beunderstood that the materials described for FIGS. 1 and 2 are examplesonly and the stack could include any number of different materials.

The mask 110 includes a plurality of apertures 112A, 112B formedtherein. As used herein, an “aperture” can refer to, for example, anopening extending partially or completely through the mask, or any otherfeature configured to purposefully allow certain radiation, or portionsthereof, to pass through the mask. In the embodiment shown in FIG. 1,there are two apertures 112A and 112B that are shaped as mirror imagesof each other across line B. Each of the apertures 112A, 112B includes aplurality of finger apertures 114 joined by a cross-connecting aperture116 arranged substantially perpendicularly to and at one edge of thefinger apertures 114.

In the embodiment shown in FIG. 1, the apertures 112A, 112B each havefour finger apertures 114. In other embodiments, the apertures 112A and112B may have fewer or a greater number of finger apertures 114, forexample, two, three, five, six, or more. In various embodiments, thewidth of the fingers w, the width of the cross-connector aperture c, andthe spacing between the apertures s, may all be modified as desired. Inthe embodiment shown in FIG. 1, the width w of the finger apertures 114is greater than the width z of the portion of the mask 110 separatingthe finger apertures 114. In yet other embodiments, the shape of thefinger apertures 114 may be modified to change the shape of the finalvias 132 (FIG. 9). In the embodiment shown in FIG. 13, multiple pairs ofcorresponding apertures 1312A, 1312B, 1314A, 1314B, 1316A, and 1316B canbe arranged in a single mask 1310 to form contacts at various locationson a single integrated circuit or on a number of integrated circuitsarranged on a same die. The pattern shift for the two exposures can alsobe used to adjust final via shape and size.

As shown in FIG. 3, the photoresist material 120 is exposed toradiation, such as light, during a first exposure step. First portions122A, 122B of the photoresist material 120 receiving certain radiationthrough the apertures 112A, 112B and areas outside the mask 110 areformed into a pattern 121 (FIG. 4) that remains substantially intactafter the photoresist material 120 is treated, for example, by a solventin a later step. FIG. 4 shows the photoresist material 120 underneaththe mask 110. Areas 125 of the photoresist material 120 not exposed tothe radiation will not be removed by a later step.

As shown in FIG. 5, the mask 110 is shifted relative to the firstpattern 121 so that, for example, the apertures 112A, 112B in the mask110 overlap some part of the first portions 122A, 122B of the firstpattern 121. In the embodiment shown in FIG. 5, the mask 110 is shiftedto the right relative to the first pattern 121 by a distance X and downrelative to the first pattern 121 by a distance Y.

As shown in FIG. 6, the photoresist material 120 is exposed to radiationduring a second exposure step. Second portions 124A, 124B of thephotoresist material 120 receiving certain radiation through theapertures 112A, 112B are formed into a second pattern 123, overlappingthe first portions 122A, 122B of the first pattern 121, that remainssubstantially intact after treatment (e.g., developing).

As shown in the top down view of FIG. 7, the mask 110 (FIG. 6) isremoved over from the photoresist material 120. The unexposed portions126 of the photoresist material 120 arranged between the first pattern121 and second pattern 123 are removable and form the footprints for theareas to be etched into vias. Due to the shifting of the mask, theheight z of the unexposed portions 126 is equal to the distance zseparating the horizontal apertures (FIG. 1). Exposure, dose, andillumination will also influence height and width of unexposed regions.Adjustments or variation in the height of the unexposed portions z canbe used to modify unexposed dimensions.

As shown in the top down view of FIG. 8, the unexposed portions 126(FIG. 7) of the photoresist material 120 are removed using methods knownin the art, such as treating with a solvent, to form openings 128 in thephotoresist material 120 to expose the dielectric material 130. Thedielectric material 130 is then etched using the remaining photoresistmaterial 120 as a mask, such as using either a wet or dry chemical etchto form the vias 132 in the dielectric material 130 and expose theconductive layer 140. As shown in the top down view of FIG. 9, theremaining photoresist 120 is removed to expose the dielectric material130 having a plurality of vias 132 formed therein. The vias 132 may thenbe filled with conductive material as is known in the art to formelectrical connections to portions of the conductive layer 140. Asdiscussed above, the conductive layer 140 may be made up of a pluralityof closely spaced conductive lines (not shown) to which the conductivematerial in the vias 132 may be connected. Additional conductivematerials or other features may be formed over the electricalconnections.

FIGS. 10, 11, and 12 each show further embodiments of masks 1010, 1110,1210, respectively, that may be used in the method described above inFIGS. 1-9. The mask 1010 of FIG. 10 includes a number of elongatedapertures 1010A, 1010B, separated by and extending away from a centralsolid portion 1016 of the mask 1010. The mask 1110 of FIG. 11 includes anumber of elongated apertures 1112A, 1112B, extending away from acentral solid portion 1116 of the mask 1110, and joined together at oneend by a connecting aperture portion 1117A, 11117B. The mask 1210 ofFIG. 12 is similar to the mask 1110 of FIG. 11, except that it alsoincludes a number of protrusions 1218 arranged at the intersection ofthe apertures 1110A, 1110B and the central portion 1116.

By the embodiments described above, the limitations imposed on the sizeof patterns made by photolithographic techniques may be overcome andpatterns smaller than the minimum pitch for a given mask may beproduced. The patterns may then be formed into features such as vias andfilled with conductive material to form electrical connections that aresmaller than connections that could be produced using a single mask.

The above description and drawings are only to be consideredillustrative of specific embodiments, which achieve the features andadvantages described herein. Modifications and substitutions forspecific conditions and materials can be made. Accordingly, theembodiments are not considered as being limited by the foregoingdescription and drawings, but is only limited by the scope of theappended claims.

1. A method of forming a pattern in a material, the method comprising:exposing first portions of a first material to radiation through atleast two apertures of a mask arranged over the first material; shiftingthe mask so that the at least two apertures overlap a portion of thefirst portions of the first material; and exposing second portions ofthe first material to radiation through the at least two apertures,wherein the first portions and the second portions overlap in such a waythat non-exposed portions of the first material are arranged between thefirst portions and second portions; and removing the non-exposedportions or exposed portions of the first material.
 2. The method ofclaim 1, wherein the removing act forms a plurality of openings in thefirst material.
 3. The method of claim 2, wherein a second material isprovided below the first material and said method further comprisesetching the second material through the openings in the first materialto form a plurality of features in the second material.
 4. The method ofclaim 1, wherein shifting the mask comprises shifting the maskhorizontally and vertically.
 5. The method of claim 1, wherein removingthe non-exposed portions of the first material comprises exposing thenon-exposed portions of the first material to a solvent to dissolve thenon-exposed portions of the first material.
 6. The method of claim 1,wherein the first material is a photoresist material.
 7. The method ofclaim 1, wherein the at least two apertures are mirror images of eachother.
 8. The method of claim 1, wherein each of the at least twoapertures include a plurality of substantially horizontal aperturesspaced apart from each other and a substantially vertical apertureoverlapping ends of the substantially horizontal apertures.
 9. Themethod of claim 8, wherein the width of the horizontal apertures islarger than the distance separating the horizontal apertures.
 10. Themethod of claim 8, wherein the mask is shifted in a horizontal andvertical direction such that the second portions of the of the firstmaterial formed through the horizontal apertures overlap the areasbetween the first portions of the first material formed through thehorizontal apertures.
 11. The method of claim 8, wherein the height ofthe removable portions of the first material is equal to the distanceseparating the horizontal apertures.
 12. A method of forming openings ina material to be patterned, the method comprising: exposing aphotoresist material over a material to be patterned through at leasttwo apertures of a mask over the photoresist material during a firstexposure to form first portions of the photoresist material; shiftingthe mask vertically and horizontally so that the at least two aperturesoverlap a portion of the first portions; exposing the photoresistmaterial through the at least two apertures during a second exposure toform second portions of the photoresist material; removing removableportions of the photoresist located between the overlapping firstportions and second portions of the photoresist to form openings in thephotoresist material; and etching the material to be patterned throughthe openings in the photoresist to form a plurality of openings in thematerial to be patterned.
 13. The method of claim 12, wherein theopenings are vias.
 14. The method of claim 13, further comprisingfilling the vias with conductive material to form a plurality ofelectrical connections.
 15. The method of claim 12, wherein the at leasttwo apertures are mirror images of each other.
 16. The method of claim12, wherein each of the at least two apertures include a plurality ofsubstantially horizontal apertures spaced apart from each other and asubstantially vertical aperture overlapping ends of the substantiallyhorizontal apertures.
 17. The method of claim 16, wherein the width ofthe horizontal apertures is larger than the distance separating thehorizontal apertures.
 18. The method of claim 16, wherein the mask isshifted in a horizontal and vertical direction such that the secondportions of the of the first material formed through the horizontalapertures overlap the areas between the first portions of the firstmaterial formed through the horizontal apertures.
 19. The method ofclaim 16, wherein the height of the removable portions of the firstmaterial is equal to the distance separating the horizontal apertures.20. The method of claim 12, wherein removing the removable portions ofthe photoresist comprises exposing the photoresist to a solvent todissolve the removable portions of the photoresist.